4-59 fast and ls ttl data 8-line to 3-line priority encoder the mc54/74f148 provides three bits of binary coded output representing the position of the highest order active input, along with an output indicating the presence of any active input. it is easily expanded via input and output en - ables to provide priority encoding over many bits. ? encodes eight data lines in priority ? provides 3-bit binary priority code ? input enable capability ? signals when data present on any input ? cascadable for priority encoding of n bits connection diagram dip (top view) 15 16 14 13 12 11 10 2 1 3 4 5 6 7 v cc 9 8 eo gs i 3 i 2 i 1 i 0 a 0 i 4 i 5 i 6 i 7 e1 a 2 a 1 gnd note: this diagram is provided only for the understanding of logic operations and should not be used to estimate propagation delays. logic diagram i 0 i 1 i 2 i 3 i 4 i 5 i 6 i 7 e1 eo gs a 0 a 1 a 2 (10) (11) (12) (13) (1) (2) (3) (4) (5) (15) (14) (9) (7) (6) mc54fxxxj ceramic mc74fxxxn plastic mc74fxxxd soic mc54/74f148 8-line to 3-line priority encoder fast ? shottky ttl j suffix ceramic case 620-09 n suffix plastic case 648-08 16 1 16 1 ordering information 16 1 d suffix soic case 751b-03 logic symbol i 0 i 1 i 2 i 3 i 4 i 5 i 6 i 7 e1 eo a 0 a 1 a 2 gs 5 4 3 2 1 13 12 11 10 14 6 7 9 15 v cc = pin 16 gnd = pin 8
4-60 fast and ls ttl data mc54/74f148 guaranteed operating ranges symbol parameter min typ max unit v cc supply voltage 54, 74 4.5 5.0 5.5 v t a operating ambient temperature range 54 55 25 125 c 74 0 25 70 i oh output current e high 54, 74 1.0 ma i ol output current e low 54, 74 20 ma functional description the f148 8-input priority encoder accepts data from eight active low inputs (i 0 i 7 ) and provides a binary representa- tion on the three active low outputs. a priority is assigned to each input so that when two or more inputs are simultaneously active, the input with the highest priority is represented on the output, with input line 7 having the highest priority . a high on the enable input (e1 ) will force all outputs to the inactive (high) state and allow new data to settle without producing erroneous information at the outputs. a group signal output (gs ) and enable output (eo ) are provided along with the three priority data outputs (a 2 , a 1 , a 0 ). gs is active low when any input is low ; this indicates when any input is active. eo is active low when all inputs are high. using the enable output along with the enable input allows cascading for prior - ity encoding on any number of input signals. both eo and gs are in the inactive high state when the enable input is high. function table inputs outputs e1 i 0 i 1 i 2 i 3 i 4 i 5 i 6 i 7 gs a 0 a 1 a 2 eo h x x x x x x x x h h h h h l h h h h h h h h h h h h l l x x x x x x x l l l l l h l x x x x x x l h l h l l h l x x x x x l h h l l h l h l x x x x l h h h l h h l h l x x x l h h h h l l l h h l x x l h h h h h l h l h h l x l h h h h h h l l h h h l l h h h h h h h l h h h h h = high v oltage level; l = low v oltage level; x = don't care 0 1 2 3 4 5 6 7 e1 a 2 a 1 a 0 gs 'f148 enable msb lsb flag a 3 a 2 a 1 a 0 0 1 2 3 4 5 6 7 e1 a 2 a 1 a 0 gs 'f148 'f148 figure 1. application: 16-input priority encoder eo
4-61 fast and ls ttl data mc54/74f148 dc characteristics over operating temperature range (unless otherwise specified) limits symbol parameter min typ max unit test conditions v ih input high voltage 2.0 v guaranteed input high voltage v il input low voltage 0.8 v guaranteed input low voltage v ik input clamp diode voltage 1.2 v i in = 18 ma v cc = min v oh output high voltage 54, 74 2.5 3.4 v i oh = 1.0 ma v cc = 4.50 v 74 2.7 3.4 v i oh = 1.0 ma v cc = 4.75 v v ol output low voltage 0.35 0.5 v i ol = 20 ma v cc = min i ih input high current 20 m a v cc = max, v in = 2.7 v 100 m a v cc = max, v in = 7.0 v i il i 0 , e1 0.6 ma v cc = max, v in = 0.5 v i il i 1 i 7 1.2 ma v cc = max, v in = 0.5 v i os output short circuit current (note 2) -60 150 ma v cc = max, v out = 0 v i cc power supply current 23 35 ma v cc = max, v in = 4.5 v notes: 1. for conditions shown as min or max, use the appropriate value specified under guaranteed operating ranges. 2. not more than one output should be shorted at a time, nor for more than 1 second. ac characteristics 54/74f 54f 74f t a = +25 c v cc = +5.0 v c l = 50 pf t a = 55 c to +125 c v cc = 5.0 v 10% c l = 50 pf t a = 0 c to 70 c v cc = 5.0 v 10% c l = 50 pf symbol parameter min typ max min max min max unit t plh propagation delay 3.5 7.0 9.0 3.5 11 3.5 10 ns t phl i n to a n 4.0 8.0 10.5 4.0 13 4.0 12 ns t plh propagation delay 2.5 5.0 6.5 2.5 8.5 2.5 7.5 ns t phl i n to eo 2.0 5.5 7.5 2.0 9.5 2.0 8.5 ns t plh propagation delay 3.0 7.0 9.0 3.0 11 3.0 10 ns t phl i n to gs 2.0 6.0 8.0 2.0 10 2.0 9.0 ns t plh propagation delay 3.5 6.5 8.5 3.5 10.5 3.5 9.5 ns t phl e1 to a n 3.0 6.0 8.0 3.0 10 3.0 9.0 ns t plh propagation delay 2.5 5.0 7.0 2.5 9.0 2.5 8.0 ns t phl e1 to gs 3.0 6.0 7.5 3.0 10 3.0 8.5 ns t plh propagation delay 3.0 5.5 7.0 3.0 9.0 3.0 8.0 ns t phl e1 to eo 4.5 8.0 10.5 4.5 13 4.5 12 ns
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